Contributions of Atlantic Ocean to June - August rainfall over Uganda and Western Kenya

Ogwang, Bob and Ongoma, Victor and Gitau, Wilson (2016) Contributions of Atlantic Ocean to June - August rainfall over Uganda and Western Kenya. Journal of the Earth and Space Physics, 41 (4). pp. 131-140. ISSN 0378-1046

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Abstract

This study investigates the contributions of Atlantic Ocean to June-August rainfall over Uganda and western Kenya (KU). The study has utilized the datasets including precipitation from the Global Precipitation Climatology Centre, North Atlantic Oscillation Index (NAOI), South Atlantic Ocean Dipole Index (SAODI), ERA-interim reanalysis, and the Atlantic Ocean Sea Surface Temperature (SST). Singular value decomposition (SVD), composite analysis and correlation analysis are used to achieve the objective of the study. Results show that the recent extreme rainfall events of June - August (JJA) season were experienced in 2007 (above normal) and 2009 (below normal). Further analysis reveals that there are significant coupled modes of variability; the first mode explains 32% whereas the second mode explains 16% of the total covariance. The first SVD mode captures the positive phase of the South Atlantic Ocean Dipole (SAOD) over Atlantic Ocean. This is associated with positive anomaly of rainfall in most parts of KU. The second SVD mode captures the negative phase of SAOD. The North Atlantic Ocean Index (NAOI) exhibits a significant positive correlation of coefficient ≥ 0.3 with the mean JJA rainfall anomaly over most parts of KU at 95% confidence level. The correlation between the mean JJA rainfall over most parts of KU and NAOI is higher compared to that with SAODI. The dominant moisture source in the region during JJA season is the Atlantic Ocean and the Congo rainforest. The findings from this study provide insight into the influence of Atlantic Ocean on the mean JJA rainfall over KU. The study recommends further research on the utilization of NAOI and SAODI as predictors of the JJA seasonal rainfall over the study area. The production of the JJA seasonal rainfall forecast in the region will enhance better utilization of water resources in the region.